The term “organic feed materials” includes biomass, peat, coal and oil shales/sands, plastic waste materials, and also includes blends of these feed materials.
The present invention relates particularly, although by no means exclusively, to a method and an apparatus for drying and pyrolysing organic feed materials in the form of biomass and coal to produce valuable products such as oil, gas and char.
The term “biomass” is understood herein to mean living or recently living organic matter. Specific biomass products include, by way of example, forestry products (including mill residues), agricultural products, biomass produced in aquatic environments such as algae, agricultural residues such as straw, olive pits and nut shells, animal wastes, municipal and industrial residues.
The term “coal” is understood herein to include, by way of example, peat, brown coal, black coal, and a range of products referred to as “coal wastes”.
The term “oil shales” is understood herein to include by way of example any geological sedimentary material containing a usable proportion of organic molecules.
The following description focuses on pyrolysis of organic feed materials in the form of biomass and coal. However, it is understood that the present invention is equally applicable to drying solid organic feed materials and has important applications in drying materials such as brown coal, with minimal if any pyrolysis, that have significant amounts of retained or bound water.
Pyrolysis of biomass and coal has been proposed as an option for producing valuable products such as oil, gas and char.
The term “pyrolysis” is understood herein to mean thermal decomposition of organic material in the absence of or with limited supply of an oxidising agent such that only partial gasification is possible. This could range from “mild pyrolysis” leading to drying and partial thermal decomposition, to “full pyrolysis” resulting in oil, gas and char products. The main products of pyrolysis are gases, liquids, and char. Typically, the gases include carbon monoxide, carbon dioxide, hydrogen, and hydrocarbons. Typically, the liquids include water, tars, and oils. Lower processing temperatures and longer vapour residence times favour the production of char—such processing is often referred to as “slow pyrolysis”. Moderate temperatures and short vapour residence times favour the production of liquids—such processing is often referred to as “fast pyrolysis”.
Slow pyrolysis is characterised by a relatively slow heating rate (typically less than 10° C./sec) and long gas and solids residence times, producing gas, liquids and char in approximately equal amounts. Known slow pyrolysis processes include processes based on the use of retorts, kilns, and vertical packed bed reactors.
Fast pyrolysis is characterised by rapid decomposition of biomass and the formation of more than 50% liquids, with the process heat requirements being provided from the remaining decomposition products, i.e. gas and char. Typical reported heat rates are of the order of 500° C./sec or more. Known fast pyrolysis processes include processes based on the use of bubbling fluidised beds, circulating fluidised beds, rotating cone reactors and twin screw reactors.
The known methods and apparatus for pyrolysing organic materials require high capital and/or operating costs for commercial scale production or can not be scaled up from current pilot or demonstration plant size to commercial production scale plants or are not efficient in energy terms to be viable in the short term and the longer term. This latter point will become increasingly important as there is increasing pressure for technology to operate in an energy efficient manner.
The above description is not to be taken as an admission of the common general knowledge in Australia and elsewhere.